1. Field of the Invention
The present invention pertains to a surgical applicator, and more particularly to an atrial-ventricular endocardial lead.
2. Description of the Prior Art
Early cardiac pacemakers utilized electrical stimulation of a single chamber of the heart, typically the right ventricle. Single chamber stimulation is still the most prevalent pacing technique. However, a number of medical conditions are more effectively treated using stimulation of two chambers of the heart or by sensing in one chamber and stimulating another. These techniques typically utilize the right ventricle and the right atrium, and generally use a separate pacing lead for each chamber. This approach is relatively convenient in epicardial applications, but is often problematical in endocardial applications in which the leads are inserted transvenously. Single pass atrial-ventricular pacing leads have been designed to avoid these problems.
Because internal heart anatomy varies among individuals, a number of atrial-ventricular leads utilize atrial and ventricular electrodes which are adjustable relative to one another. Several current designs encase both atrial and ventricular conductors in a commmon outer sheath with either the atrial or the ventricular conductor slideably mounted within the outer sheath, allowing axial adjustment of the relative positions of the electrodes. In present designs, this adjustment method often results in difficulties or complexities in attaching the lead to implantable pulse generators.
An early single pass atrial ventricular lead is taught by Bures in U.S. Pat. No. 3,865,118. In this lead, the ventricular lead sheath is slideably mounted within the artial lead sheath. Electrodes are attached to the distal portions of the atrial and ventricular sheaths and electrical connectors are attached to the proximal ends of these sheaths. Movement of the ventricular electrode relative to the atrial electrode therefore results in movement of the ventricular connectors relative to the atrial connectors. Present implantable pulse generators, however, employ connector assemblies with electrical connectors in fixed relation to one another. If the arrangement of electrical connectors on the lead does not correspond to the arrangement of electrical connectors on the pulse generator, attachment to the pulse generator may be precluded. If attachment is possible, it generally requires deformation of the lead to mate the connectors, which stresses the lead and may lead to fracture of the lead conductor. Because the arrangement of connectors is variable on the Bures lead, the probability of such difficulties is increased.
Another early single pass atrial ventricular lead is taught by Sabel in U.S. Pat. No. 3,949,757. In this lead, the atrial sheath is slideably mounted within the ventricular sheath. As with the Bures lead, adjustment of the relative positions of the electrodes changes the relative positions of the electrical connectors, with the disadvantages discussed above.
A more recent single pass atrial ventricular lead that overcomes some of the problems of the Bures and Sabel leads is taught by Gilman in U.S. Pat. No. 4,289,144. In this lead, the ventricular sheath is slideably mounted within the atrial sheath. Mounted at the proximal end of the lead is a bifurcated connector assembly with two connector sleeves. One connector sleeve carries a connector pin coupled to the atrial electrode by means of a conductor. The proximal end of the ventricular sheath slideably protrudes from the other connector sleeve. After the lead is adjusted, the protruding ventricular sheath and the conductor within it are trimmed and an electrical connector pin is attached to the proximal end of the conductor, a time consuming procedure. Because the arrangement of the two connector pins then corresponds to the arrangement of the electrical connectors on typical pulse generators, attachment is easily accomplished without stress to the lead. After attachment, further adjustment of the lead is precluded, as the ventricular sheath and conductor are then fixed.
A further problem common to several single pass A-V leads is that of sealing the lead at the exit point of the inner sheath. In leads such as the Gilman lead, where a conductor is exposed to the lumen of the outer sheath, a fluid path from that lumen to the exterior of the lead raises the risk of current leakage.